Generally, a substrate, such as a semiconductor wafer, is subjected repeatedly to film formation and pattern etching to form a plurality of desired elements on the substrate to fabricate a semiconductor integrated circuit.
Usually, a barrier metal layer is interposed between wiring lines interconnecting the elements and a layer underlying the wiring lines, such as the substrate or a Si-containing layer, to prevent the diffusion of silicon from the substrate or the Si-containing layer into the wiring lines and that of a material forming the wiring lines into the substrate or the Si-containing layer. The material of the barrier metal layer must have excellent corrosion resistance, not to mention low electrical resistance. Nitrides of metals having a high melting point, such as Ti (titanium), W (tungsten) and Mo (molybdenum), are used generally as barrier metals meeting the foregoing requirement when the wiring lines are aluminum wiring lines or tungsten wiring lines, which are used prevalently. There is a tendency to use Ti films or TiN films because of their satisfactory characteristics, such as electrical and corrosion-resistant properties.
A Ti film or a TiN film, as a barrier metal layer, is formed by a CVD process (chemical vapor deposition process) which is carried out in a high-temperature atmosphere of temperatures in the range of about 500° C. to 700° C., is capable of effectively filling up contact holes and via holes of a large aspect ratio, and has characteristics satisfactory for use in combination with aluminum or tungsten.
The width of wiring lines and the like has been diminished to meet the recent growth in the number of components per integrated circuit and the progressive miniaturization of integrated circuits. For example, the width of wiring lines desired in recent years is 0.2 μm or below. The enhancement of the operating speed of integrated circuits, as well as the increase of the number of components, has been intensely desired. Under such circumstances, comparatively inexpensive copper having a low resistivity has become a prospective wiring material capable of replacing aluminum.
However, as is generally known, copper (Cu), similarly to aluminum (Al), is liable to migrate into silicon and diffuses easily at low temperatures. Therefore, the performance of Ti or TiN barrier films used in combination with Cu wiring lines is unsatisfactory. Therefore, barrier metal layers of those barrier metals must be formed in a considerably large thickness to achieve a satisfactory barrier performance. If such a barrier metal layer having a large thickness is used in a multilayer integrated circuit device, in which wiring lines and a barrier metal layer must be formed in a section of a limited height, the sectional area of the wiring lines must be reduced accordingly. Consequently, the wiring lines have a high resistance. Thus, there has been a strong demand for the development of a barrier metal layer effective for use in combination with copper wiring lines.